The present invention relates to an improved retractor (a winding device) for use in a seat belt device and, in particular, to an improved seat belt retractor which includes both an emergency lock mechanism and an automatic lock mechanism. In addition, the present invention also relates to a control method for controlling a seat belt retractor which includes an emergency lock mechanism, an automatic lock mechanism and an energy absorbing mechanism.
Conventionally, in a seat belt for holding an occupant and the like of a vehicle safely in the seat of the vehicle, there is provided a seat belt retractor which is structured such that, when restraining the body of the occupant, an emergency lock mechanism thereof can be operated, and, when fixing a baggage, a child seat or the like to the seat, an automatic lock mechanism can operated.
That is, the seat belt retractor of this type comprises a well-known emergency lock mechanism including lock means engageable with a winding shaft and capable of locking the rotation of the winding shaft in a webbing pull-out direction thereof and inertia sensing means for actuating the lock means in a vehicle emergency, and control means for actuating the emergency lock mechanism in accordance with the winding condition of the webbing to thereby cause the lock means to move to an engaging position or a non-engaging position properly with respect to the winding shaft, while the control means brings the lock means into engagement with the winding shaft to thereby lock the rotation of the winding shaft in the webbing pull-out direction thereof, so that the automatic lock mechanism can be actuated. And, conventionally, there have been proposed various seat belt retractors each of which, due to provision of the above-mentioned control means, can be surely switched from an emergency lock retractor over to an automatic lock retractor.
On the other hand, when the shock caused by a collision is extremely great, the tension of a webbing increases with the passage of time after the collision to thereby produce a sudden deceleration in the body of the occupant, so that a load to be applied to the occupant from the webbing becomes very large. In view of this, there have also been proposed various kinds of seat belt devices each structured such that it include an energy absorbing mechanism which, when a load acting on the webbing becomes equal to or greater than a preset given value, pulls out a seat belt by a given amount to thereby absorb the shock given to the body of the occupant so as to be able to protect the occupant body against the shock more surely. As the seat belt retractor having such structure, there is known the energy absorbing device designed especially for a safety belt which is disclosed in U.S. Pat. No. 3,741,494 to Fiala.
The above-mentioned energy absorbing device comprises a winding member (a bobbin) serving as a part to which the energy absorbing device transmits a force, and a holder (a retractor base) relatively rotatable with respect to the winding member, while a torsion bar is interposed between the holder and winding member. In this device, if, after the rotation of the winding shaft is caused to stop in a vehicle emergency, a load is further applied to the lock means, the torsion bar is twisted about its own axis, so that the shock energy given to the occupant body can be absorbed as the deformed version of the work of the torsion bar.
The seat belt retractor including the energy absorbing mechanism of the above-mentioned type pulls out the seat belt by a given amount when the load acting on the webbing becomes greater than the preset given value, while the pull-out amount of the seat belt is generally set according to the size of a space formed in front of an occupant seated in the seat.
In this structure, when a child seat or the like bulkier than the body of the occupant is fixed to the seat, if the seat belt is pulled out in a vehicle emergency, then there is a possibility that the child seat or the like can be contacted with the dashboard of the vehicle.